Sunday, July 15, 2012

AutoGardens - Mid July 2012- Goodbye Archimedes!

Goodbye Archimedes!

[see photos near the end of this blog]

While constructing the 13 or so AutoGarden systems for the testing this year, I couldn't shake the feeling that even though I had simplified the system considerably, there must be an even better way.  About a dozen different ideas were jostling around in my brain and it was only in the middle of a sleepless night that I came up with my latest idea.  It is much simpler than the Archimedes water lifter, is easy to make, and requires no motors or batteries.  In the last section of this blog I will describe a setup that should water my plants ALL SUMMER automatically.

If you have ever heard of a pinch valve you already know about the key element of the new system.  A pinch valve is a piece of flexible tubing that allows water to flow through it.  Upon pinching the tubing, the water flow stops.  Simple rubber hose makes great pinch valves.

The new idea in the AutoGardens is the use of pinch valves to act as float valves and maintain a layer of water about 2 to 3 cm in the tray.  The source of the water is a 32 gallon garbage can filled with water and a siphon tube to a horizontal 1/2" PVC pipe.  At each AutoGarden rack, a fitting is located that branches off the 1/2 inch PVC pipe with a small length of rubber tubing.  The rubber tubing goes to the float valve in the tray.

The float valve is made from a piece of 1 inch thick styrofoam board about a square foot in area.  The shape doesn't matter much.  On top of the piece of foamboard is a 5/16" piece of PVC board that serves as a stiffener of the foamboard and the bottom surface of the pinch valve.  The rubber tubing is placed on top of the PVC board and a small piece of 5/16 inch PVC board is held above the tubing.  The board is held in a vertical position and the bottom edge is sanded down to form a fairly sharp edge.  The sharpness of the edge focuses the thrust of the board into a narrow line and minimizes the amount of floating styrofoam needed to shut the valve.

The final element in the system is a wooden beam about 1" x 1" and 24" long that straddles the tray and holds the vertical  PVC board.

Construction of the valve is very easy and uses simple tools.  One big advantage of the new system is that the  water tanks are no longer part of the rack.  Also the trays no longer have to have sections cut out for the Archimedes water lifter mechanism.  They can be simple 24" by 72" trays that are water tight and have side walls two inches high.  No bottom drains are required.
Pinch valve type float valve.  The pink foamboard floats on the water in the tray.  When the water level rises, the plastic board pushes the rubber tube up into the stationary "knife edge" and closes off the water flow.  When the water level goes down again (because of evaporation or uptake from the plant pots) the valve opens.

Connection of the rubber hose to the horizontal feeder tube.  I used a standard coupling fitting, drilled a hole in its middle and then pressed a small length of copper tubing into the hole.  

The connections of the autogarden trays to the garbage can.  

Last note
For my system at my home I have eliminated the garbage can and use a siphon tube that connects the tank of my toilet to the autogarden system.  As water is used by the autogarden racks the toilet tank is constantly refilled so there is no worry about the system running dry.  I anticipate the system should run ALL SUMMER without any concern that the plants will dry out.